Friction elements for braking rotary bodies

ABSTRACT

Friction elements for braking rotary bodies, such as wheels in railway cars, electric cars and motorcars, contains 50 - 100% by weight of aluminum and said elements may be aluminum alloys or aluminum compositions. These elements may be used alone by directly sliding on a wheel or together with a conventional brake, or for a brake shoe in a disc brake.

United States Patent 11 1 Yamaguchi et a1.

[ Feb. 12, 1974 FRICTION ELEMENTS FOR BRAKING ROTARY BODIES [73]Assignee: Nippon Carbon Company, Limited,

Tokyo, Japan [22] Filed: Nov. 29, 1971 [2]] Appl. No.1 202,857

I [30] Foreign Application Priority Data 3,092,214 6/1963 Batchelor eta1 188/251 M X 3,318,423 /1967 Dunki 188/251 M 3,003,588 10/1961Huntress 188/251 M X 3,306,401 2/1971 Dasse 188/251 M 3,371,756 3/1968Spitz i 188/251 M 761,384 5/1904 Lambert 188/251 M PrimaryExaminer-Allen N. Knowles Assistant ExaminerGene A. Church Attorney,Agent, or FirmStevens, Davis, Miller &

Mosher Dec 5, 1970 Japan;.. 45407190 [57] ABSTRACT Dec. 25, 1970 Japan-118141 Friction elements for braking rotary bodies, such as wheels inrailway cars, electric cars and motorcars, 188/251 g z gg gg contains byweight of aluminum and said I elements y be aluminum alloys or aluminum[58] Fleld of Search 188/251 l92/ l07 M positions. These elements may beused alone by di rectly sliding on a wheel or together with a conven-[56] uNlTE g gi i gs gziENTs tional brake, or for a brake shoe in a discbrake.

3,478,849 11/1969 Hahm 188/251 M X 10 Claims, 7 Drawing Figures Q 5 0.4It i 1; 05 Dry cana /non k Q 0,2 5 We! condmon 0./

.Q a: a 1 l I l 8 50 I00 I50 200 250 Velocity (Km/Hr.) f

FRICTION ELEMENTS FOR BRAKING ROTARY BODIES The present inventionrelates to novel friction elements and particularly to friction elementscomposed of aluminum-containing alloy or composition.

,The object of the present invention is to provide friction elements bywhich a brake can be satisfactorily operated even upon driving in a highspeed and an excellent braking function can be obtained when using inthe presence of water,- for example, under raining or in water.

As the friction elements, cast iron, copper series sintered alloy, resinmold and the like have been known but they have some drawbacks and havenot been fully satisfied. Particularly, the brake working has recentlybecome very severe in the condition but the friction elements fit forsuch condition have never been developed. For example, the-velocity ofcars has become higher, so that the requirements in the brake workingare severe and the brake must be operated securely under raining or inwater but materials satisfying these requirements have never beenobtained.

For example, various brakes have been used in order to decrease orcontrol the speed of rotary portions of machines, installations and thelike and among them a friction brake which utilizes the frictional forcegenerating at contacting portion between solids, has been most used. Thevelocity of wheels in railway cars or electric cars is controlled'by thefrictional force generated by contacting the side face of discs engagingwith the wheels with a brake.

However, this brake is made of materials mainly selected in view of thefrictional properties and can develop the frictional force fully in fineweather but lowers the frictional force under a wet condition.Accordingly, in the case of rolling stocks, such as railway cars andelectric cars which need a high frictional force either in the fineweather or in raining, the decrease of the frictional force is animportant problem.

Furthermore, recently the rotary portions in machines get a high speedand particularly the rolling stocks and motorcars in a high speedrequire the control of speed under the most severe conditions andfriction elements satisfying these reqirements have been demanded.

In the relation of the wheel velocity to the coefficient of friction inthe well known brake, the coefficient of friction lowers under a wetcondition and at a higher speed. Therefore, in the recent high speedcars, the brake pressure is controlled with reference to some degree ofexperience or known data considering the variation of weather, wherebythe velocity is controlled. Furthermore, in motorcars, the brakemechanism itself is housed in a casing and therefore the braking is notinfluenced by weather as in the rolling stocks, but in the raining,water enters into the casing and in winter the brake becomes wet due tofrost and the same problem as in the rolling stocks occurs and thecontrol of speed depends upon the technic of the driver resulting intoan accident in raining.

In the rolling stocks in running on rails, a frictional force isgenerated between the wheels and the rails and this causes attractingforce and the running is made and a braking force is generated and astopping is effected. Namely, the rotating force of wheels is applied onthe rails by the frictional force between the wheels and the rails andthen the reaction force is subjected to the wheels and the rolling stockis accelerated and runs, while when a force for stopping the rotation ofwheels is applied, the stopping force is applied on the rails by theabove described frictional force and the reaction force is applied tothe wheels and the velocity of the rollling stock is decreased; Howeverin the above described frictional force there is a limitation and when atoo large braking force is applied to the wheels, they slip and thefrictional force causing the slip is referred to as critical frictionalforce. A variety of investigations have been made with respect to thecritical frictionalforce. For example, the critical frictional forcemainly depends upon the physical properties between the rails and thewheels and as this value the coefficient of friction must be at least0.15. When the coefficient of friction is less than 0.15, the slipoccurs, and even if the braking is applied, the speed of the rollingstock cannot be controlled and the slip brings about the damage ofwheels and rails.

It was determined with respect to the real railway cars whether theabove described relation (at least 0.15 of coefficient of friction) ismaintained or not and the result as shown in FIG. 1 was obtained. FIG. 1is a graph for showing the variation of the coefficient of friction atvarious velocities of a rolling stock, when the condition of railsvaries. As seen from FIG. 1, as the speed increases, the coefficient offriction decreases and when the rails are under a wet condition, thecoefficient of friction lowers and for example when the speed exceedsabout 70 Km/hr, the coefficient of friction lowers to less than 0.15.However, recently the speed of rolling stocks is higher and in manycases the speed exceeds Km/hr, and the prevention of slip of wheels inthe driving under wet condition (in raining), particularly in thecontrol of speed by means of a brake has been an important problem.

The present invention is to provide novel friction elements by whichthese previous drawbacks are obviated. Namely, the friction elements ofthe present invention are excellent in the braking in a high speeddriving and show a noticeable function in the braking in the presence ofwater.

The friction elements of the present invention are applied for thefollowing uses.

l. The brake for stopping the wheels is composed of the friction elementof the present invention, which comes into a direct contact with thewheels.

2. The conventional brake and the friction element of the presentinvention are used together to improve the friction between the railsand the wheels.

3. The friction element is used as a brake shoe and is provided on adisc brake.

When the friction element according to the present invention is used asa brake shoe in the above described item (3),the brake shoe may beconstituted with the friction element of the present invention alone orwith both the friction element and a conventional brake shoe, forexample, composed of copper series sintered alloy. In this case, thefriction element of the present invention and the conventional brakeshoe may be arranged either in adjacent relation or in a space.

The inventors have foundthat a material having at least 50% by weight ofaluminum shows excellent properties as such friction element.

Namely, the friction elements of the present invention are as follows:

100% aluminum.

Aluminum alloy containing at least 50% by weight of aluminum.

Aluminum composition containing at least 50% by weight of aluminum.

The friction elements may be shaped articles (compression, casting andthe like), sintered alloys or powders.

An explanation will be made with respect to the friction mechanism ofthe friction elements of the present invention hereinafter.

Aluminum constituting the friction element easily forms hydroxide due towater and when this hydroxide is subjected to a contact friction betweensolids, the hydroxide is easily peeled and fallen off from the frictionelement and a part of peeled hydroxide deposits on a partner contactingwith the friction element.

For example, when the friction element according to the presentinvention is used as a brake shoe in a disc brake, hydroxide formed onthe brake shoe due to water peels off and deposits on the brake disc andthis hydroxide is further exposed to water, so that the surface isstabilized and the hydroxide forms rigid projections. When such rigidprojections are formed on the surface of the partner to be contactedwith the friction element, the water film formed between the brake discand the brake shoe is broken and the friction brake acts as under thedry condition and the coefficient of friction in the high speed isstabilized by the presence of the projections. Such a function also canbe obtained when the friction element of the present invention is usedas a brake shoe together with a conventional brake shoe.

When the brake for stopping the wheels is composed of the frictionelement of the present invention and this brake is directly contactedand slidden with the wheels to control the velocity, aluminumconstituting the friction element forms also hydroxide due to water asdescribed above. The hydroxide is apt to be bonded to the wheel composedof iron, and aluminum hydroxide deposited on the wheel has a ductilityand therefore is easily transformed by the compression force of thebrake against the wheel or the compression force between the wheel andthe rail and the depositing area increases. Aluminum hydroxide depositedon the wheel surface is put in water successively under a wet condition,so that the hydroxide on the surface is further stabilized and becomesrigid and forms projections. When the projections are formed on thewheel surface, the water film to be formed between the wheel and therail is broken and the wheel contacts with the rail through the abovedescribed projections formed on the wheel. Accordingly, when theprojections are increased, the solid contacting area increases andconsequently the frictional force is improved. However, the depositedprojections do not parmanently remain on the wheel surface and are wornaway in the powder form and fallen gradually, while the hydroxide isalways supplemented to the wheel from the friction element and thestable frictional force may be maintained.

Moreover, in the case of braking the wheels, ifa conventional brake isused and further the friction element of the present invention iscompressed against the wheels, a part of hydroxide formed due to wateras described above deposits on the wheels and forms the projections,which break the water film between the wheel and the rail and the waterfilm between the wheel and the brake and therefore the wheel and thebrake or the wheel and the rail contact with each other through thealuminum hydroxide projections and the frictional force is furtherimproved.

5 On the contrary, in a conventional system a water film is formedbetween the sliding members and a kind of liquid lubrication is formedand the coefficient of friction lowers.

However, according to the present invention alumi- 0 num constitutingthe friction element forms aluminum hydroxide and the hydroxide is aptto bond to a partner contacting with the friction element, which iscomposed of iron, and further has a high ductility, so that afterdeposited on the partner, the depositing area extends and consequentlythe coefficient of friction increases.

When the friction element contains at least 50% by weight of aluminumand has a certain degree of mechanical strength, the object of thepresent invention can be attained. The shaping process of the frictionelement composed of aluminum alloy may be any one of casting andsintering means, In addition,the friction element may be formed bymolding a mixture of powdery aluminum or aluminum alloy with carbon,asbestos, silica, alumina, iron oxide or sand together with a binder ofthermosetting synthetic resins, such as phenolic resin, furan resin,polyester resin, polydivinylbenzene resin and the like. When the moldingis effected by using such a binder, any shape may be easily formed.

In carrying out the present invention, the friction element may be usednot only in the shaped articles but also in the form of granule orpowder, which is supplyed to friction portions between a brake or a railand a wheel.

As mentioned above, aluminum in the friction element has the excellentbraking function. When the friction element requires a high strength anda certain degree of abrasion resistance, aluminum is added with copperand silicon and, if necessary at least one of elements selected from thegroupconsisting of magnesium, nickel, chromium, iron, lead and boronnitride is added thereto. When these elements are added to aluminum,they form a variety of compounds between aluminum (for example,intermetallic compounds). These compounds include eutectic type, solidsolution type, eduction hardening type and the like. ln the alloyscontaining at least 50% by weight of aluminum, the friction mechanism ismaintained as described above under a high speed and wet condition.

The inventors have investigated with respect to the proper compositionin the aluminum alloy, the elements to be added and the addition rangethereof and found that when said alloy contains 5085% by weight of Al,0.l-25% by weight of Si and 01-10% by weight of Cu and further, ifnecessary contains less than by weight of at least one element selectedfrom the group consisting of Mg, Ni, Cr, lr, Pb and EN, the frictionelement having the following properties can be obtained.

1. Even when said friction element is used for a rolling stock having avelocity of 100 Km/hr in raining, the coefficient of friction ismaintained at more than 0.15.

2. The worn amount of the friction element is about 10 mm in the maximumvalue per 10,000 Km of running distance of the rolling stock.

3. The mechanical strength of the friction element is more than 3,000Kg/cm in the bending strength.

4. Both the sintered alloy and the casted alloy provide the same effect.

The above described worn amount was determined as follows: The frictionelement was contacted with a rotating wheel and the running distance wascalculated from the velocity of rotation of the wheel and the wornthickness of the friction element in this case was measured. For thereference, the worn amount of a conventional friction element made ofcast-iron is 20 mm/l0,000 Km and the mechanical strength (bendingstrength) is 3,000 Kg/cm on the average.

The reason of the above limitation of the composition will be explainedhereinafter.

Aluminum is added in order to increase the frictional force andtherefore it is preferred that the amount of aluminum is larger.However, when the amount of aluminum is larger, the worn amountincreases, so that the upper limit is 85% by weight, when the aluminumalloy is used as a brake. Even when. the amount of aluminum is 50% byweight, the desired effect for improving the frictional force can beattained.

However, recently the speed of the rolling stocks is very high and it isrequired to run the rolling stocks at a velocity of more than 120 Km/hror more than 200 Km/hr, and in some cases it is required to stop the carsuddenly when the rolling stock is running at a velocity of more than200 Km/hr, and in order that such a rolling stock can be stopped inashort braking distance, the lower limit of aluminum must be about 65% byweight.

Silicon mainly serves to improve the abrasion resistance and the amountis preferred to be 01-25% by weight. Copper mainly serves to improve themechanical strength and simultaneously improves the abrasion resistanceto some extent and the amount is preferred to be 0.l-l0% by weight.

The other magnesium, nickel, chromium, iron, lead and boron nitrideserve to increase the mechanical strength and the abrasion resistanceand when the content is at most by weight, the mechanical strength andthe abrasion resistance can be improved without deteriorating thefrictional force.

The invention will now be explained with reference to the accompanyingdrawings, in which:

FIG. 1 is a graph for showing a relation of the coefficient of frictionbetween a wheel and a rail to the velocity of a rolling stock under adry condition and a wet condition; FIG. 2 isa graph for showing arelation of the coefficient of friction to the velocity of a rollingstock when aluminum sintered alloy according to the present invention isused as a friction element under a wet condition;

FIG. 3 is a front view of an embodiment of a disc brake;

FIG. 4 is a side view of the disc brake in FIG. 3 on which a brake shoeconstituted with the friction element of the present invention and abrake shoe constituted with a conventional copper series sintered alloyare arranged;

FIG. 5 is a graph for showing a relation of the coefficient of frictionto the velocity of a rolling stock when using the brake shoe as shown inFIG.- 4.

FIGS. 6-and 7 are graphs for showing relations of the coefficient offriction to the velocity of rotation of a wheel when using the frictionelement respectively.

The following examples are given for the purpose of illustration of thisinvention and are not intended as limitations thereof.

mplc 77% by weight of powdery aluminum, 4.5% by weight of powderycopper, 1 1% by weight of powdery silicon, 0.5% by weight of powderychromium, 2% by weight of powdery nickel, 0.5% by weight of magnesiumand 4.5% by weight of lead were mixed and the mixture was sintered toform a friction element. This friction element and a brake were providedon a wheel and the wheel was rotated. The revolution number was set sothat the velocity was 0200 Km/hr. During the test, water was alwayssupplied between the wheel and the rail by a hose to maintain the wetcondition and the relation between the velocity of the wheel and thecoefficient of friction when a brake was applied on the wheel, wasdetermined to obtain the result as shown in FIG. 2. From FIG. 2 it canbe seen that when the friction element of the present invention is used,the variation of the coefficient of friction is much smaller than theconventional case as shown in FIG. 1 and even in the velocity of morethan 120 Km/hr, the coefficient of friction was maintained at more than0.18.

.lizs sl of the present invention obtained by casting A brake 1% byweight of copper, 12% by weight of silicon, 1% by weight of magnesium,0.5% by weight of iron, 1.5% by weight of nickel and the balance ofaluminum and a conventional brake composed of copper series cast alloywere manufactured and a relation between a velocity and a coefficient offriction under a wet condition was determined.

- In this test, the brake was constituted as a disc brake as shown inFIG. 3. Referring to FIG. 3, l is a wheel, 2 is a shaft, 3 is a disc, 4is a brake shoe and 5 is a working mechanism of the brake. In the brakeshoe 4, a brake shoe 4a composed of the conventional copper seriessintered alloy and a brake shoe 4b composed of the above describedaluminum casted alloy were arranged contiguously.

In the conventional brake, the brake shoe 4 was constituted with thecopper series sintered alloy.

With respect to both the brakes the friction test was made under a wetcondition and the result as shown in FIG. 6 was obtained. In FIG. 5, thesolid line shows the data on the conventional brake and the broken lineshows the data on the brake of the present invention.

As seen from FIG. 5, in the conventional brake, as the velocityincreases, the coefficient of friction lowers and particularly when thevelocity is more than 60 Km/hr, the decreasing ratio becomes constantand such a brake is not suitable for a high speed rolling stock;

On the contrary, even in the brake of the present invention, thecoefficient of friction decreases as the velocity increases but thedecreasing ratio is rather small as the velocity increases andparticularly when the velocity becomes more than 80 Km/hr, thecoefficient of friction does not substantially decrease. As seen fromFIG. 5, the coefficient of friction of the brake of the presentinvention is maintained at more than 0.18 under a wet condition.

amrls 3 80% by weight of aluminum and the balance of A1- SiO Fe O andpowdery asbestos were mixed and the mixture was press molded by addingphenolic resin to form a brake shoe as shown in FIG. 4. The resultingbralte shoe was tested under the same condition as described in E xample2 and the same result as in alu minum case alloy according to thepresent invention was c ni ncd-w Example 4 76 grams of aluminum, 11 g ofsilicon, 4.5 g of copper, 0.5 g of magnesium, 2.5 g of nickel, 0.5 g ofchromium and 5 g of lead were mixed homogeneously by a mixer and theresulting mixture was molded under a pressure of 2 t/cm to form afriction element. This molded friction element was sintered underhydrogen atmosphere at 580 C for about'30 minutes. This friction elementwas tested with respect to the coefficient of friction by means of anindoor tester. Namely, a wheel was driven by a railway wheel providedwith a flywheel and to the wheel was pressed the friction ele mentmanufactured as described above and the friction element is slidden onthe wheel surface and the wheel was rotated at a velocity of 40-160Km/hr, while spraying water. In such a manner, the coefficient offriction was determined to obtain the result as shown in FIG. 6. As seenfrom FIG. 6, the coefficient of friction did not decrease to less than0.15 even at the velocity of more than 150 Km/hr and the frictionelement showed an excellent frictional force. The worn amount was 5 mmper 10,000 Km of running distance and the bending strength was 3,500Kg/cm.

FIG. 7 shows a relation between the coefficient of friction and thevelocity measured by the above described tester when using theconventional friction element and from this figure it can be seen thatthe coefficient of friction is highly influenced by the variation ofvelocity and when the velocity becomes more than 50 Km/hr, thecoefficient of friction (#1,) is less than 0.15. On the contrary, in thefriction element of the present invention, the dependency to thevelocity is very small as shown in FIG. 6 and even at a high speed, thecoefficient of friction is more than 0.15 and the frictional force hasbeen highly improved.

What is claimed is:

1. A friction element for coming forcedly into contact with at least apart of a rotary body for braking rotation thereof consisting of 50- 85%by weight of A1,

0.1 10% by weight of Cu and 0.1 25 by weight of Si. 7

2. The friction element of claim 1 Wherein said element is used as adisc brake. Y

3. The friction element of claim 1 wherein said element is used as abrake shoe together with a conventional brake shoe.

4. A friction element for coming forcedly into contact with at least apart of a rotary body for braking rotation thereof consisting of 50 85%by weight of A1, 0.1 10% by weight of Cu, 0.1 to 25% by weight of Si,and less than 10% by weight of at least one of Mg, Ni, Cr, Fe, Pb andBn.

5. The friction element of claim 4 wherein said element is used as adisc brake.

6. The friction element of claim 4 wherein said element is used as abrake shoe together with a conventional brake shoe.

7. A friction element for coming forcedly into contact with at least apart of a rotary body for braking rotation thereof and is a shapedarticle obtained by binding a mixture of at least 50% by weight of Aland the balance of asbestos, silica, alumina, iron oxide and sand with athermosetting resin.

8. The friction element of claim 7 wherein said thermosetting resin isphenolic resin, furan resin, polyester resin or polydivinylbenzeneresin.

9. The friction element of claim 7 wherein said element is used as adisc brake.

10. The friction element of claim 7 wherein said element is used as abrake shoe together with a conventional brake shoe.

2. The friction element of claim 1 Wherein said element is used as adisc brake.
 3. The friction element of claim 1 wherein said element isused as a brake shoe together with a conventional brake shoe.
 4. Afriction element for coming forcedly into contact with at least a partof a rotary body for braking rotation thereof consisting of 50 - 85% byweight of Al, 0.1 - 10% by weight of Cu, 0.1 to 25% by weight of Si, andless than 10% by weight of at least one of Mg, Ni, Cr, Fe, Pb and Bn. 5.The friction element of claim 4 wherein said element is used as a discbrake.
 6. The friction element of claim 4 wherein said element is usedas a brake shoe together with a conventional brake shoe.
 7. A frictionelement for coming forcedly into contact with at least a part of arotary body for braking rotation thereof and is a shaped articleobtained by binding a mixture of at least 50% by weight of Al and thebalance of asbestos, silica, alumina, iron oxide and sand with athermosetting resin.
 8. The friction element of claim 7 wherein saidthermosetting resin is phenolic resin, furan resin, polyester resin orpolydivinylbenzene resin.
 9. The friction element of claim 7 whereinsaid element is used as a disc brake.
 10. The friction element of claim7 wherein said element is used as a brake shoe together with aconventional brake shoe.